Of the more than 11,000 Vickers Wellington built, a full third were the MkX version. Characterised by Bristol Hercules VI or XVI engines, these planes began to pour into the Royal Air Force units in the latter part of 1942, and just a few months later twelve squadrons of the Bomber Command were partially or entirely equipped with them. The Wellington MkX was progressively replaced by four-engined bombers, but in any case it had a long lifetime. It spawned several sub-versions, in particular the anti-submarine, also supplied to Allied countries after the end of WWII. The last one was retired by the RAF only in 1953.